1. Technical Field
The present invention relates to electrophoretic display technology.
2. Related Art
When electrical fields are applied to a dispersion liquid (also referred to as a “dispersion system”) in which charged particles are dispersed in a solution (dispersion medium), the particles move (or electrophoretically migrate) in the dispersion medium by a Coulomb force. This phenomenon is called electrophoresis, and electrophoretic display devices (EPDs) that display desired information including images using the electrophoresis are known.
As an example structure of EPD, an EPD having a pair of substrates wherein a space between the substrates is divided by partitions into a plurality of spaces (cells), and a dispersion system containing charged particles (electrophoretic particles) and dispersing medium sealed in each of the cells is known. Such an EPD can be manufactured through, for example, filling the dispersion system in each of the cells, and sealing an opening section of each of the cells. For example, Japanese laid-open patent application HEI 5-165064 (Patent Document 1) and Published Japanese Translation of PCT application 2005-509690 (Patent Document 2) are related art pertaining to the method described above.
According to Patent Document 1, each cell is closed (sealed) through placing a flexible electrode plate over the cells in a manner to cover an opening of each of the cells, and applying a pressure force on an upper surface of the flexible electrode plate while pushing out excess dispersion liquid, thereby bonding them together.
On the other hand, Patent Document 2 describes a method of sealing cells using a solution or a solution mixture that is immiscibile against dispersion liquid and has a specific gravity smaller than the specific gravity of the dispersion solution, and a sealing composition containing thermoplastic elastomer. As the sealing composition has a smaller specific gravity than the specific gravity of the dispersion liquid, it is separated from and above an upper layer of the dispersion liquid, and the sealing composition in such a separated state is hardened, thereby enabling sealing of each of the cells.
It is important to prevent air (bubbles) from entering each of the cells when the dispersion liquid is contained in each of the cells. In this respect, according to the method described in Patent Document 1, sealing is conducted by mechanically applying a pressure force. Therefore air bubbles may enter in the cell depending on the amount of the dispersion liquid contained in the cell.
On the other hand, according to the method described in Patent Document 2, unless there is a sufficient difference in specific gravity between the dispersion liquid and the sealing composition, it is difficult to selectively separate the sealing composition from the upper layer of the dispersion liquid. Therefore, it is difficult to control the amount of the dispersion liquid to be sealed inside each of the cells, which may cause variations in the amount of the dispersion liquid.